1. Field of the Invention
Aspects of the present invention relate to an anode active material, and an anode and lithium battery including the anode active material.
2. Description of the Related Art
Portable electronic devices, such as cameras, notebook computers, mobile phones, and the like, are widely used, small, lightweight devices. Lithium batteries are widely used as a power source of such portable electronic devices. Thus, there is a need for lithium batteries having an increased capacity that is maintained in spite of frequent charging and discharging.
A carbonaceous material with a relatively high capacity and good cycle-life properties, e.g., graphite, is widely used as an anode active material in lithium batteries. However, graphite has a very low theoretical capacity of 372 mAh/g. Thus, much research into materials that can replace graphite has been conducted. For example, research into an anode active material capable of alloying with lithium, e.g., Si, Sn, Al, or the like, has been conducted.
However, a material that is capable of alloying with lithium, such as Si, Sn, Al, or the like, may present several problems, including a volumetric expansion during the alloying, the creation of an electrically disconnected active material in an electrode, the aggravation of electrolytic decomposition, due to an increase in surface area, and so on. In order to overcome these problems, Science, 276, 1395 (1997) discloses an amorphous Sn-based oxide, in which the particle size of Sn particles is minimized, and the agglomeration of the Sn particles, during charge and discharge cycles, is prevented, thereby leading to an improvement in capacity retention characteristics. However, the Sn-based oxide inevitably causes a reaction between lithium and oxygen atoms, which is responsible for a considerable irreversible capacity.
To address these and/or other problems, Electochem. Solid State and Lett., 2, 3 (1999), Electochem. Solid State and Lett., 2, 307 (1999), and J. Electrochem. Soc., 146, 4401 (1999) disclose an anode active material including an intermetallic compound of Sn and Si, and Cu, Fe, and Mg. The particle size of the Sn and S intermetallic compound is minimized, and the active material does not form Li2O, due to the absence of oxygen, and thereby has a high initial efficiency. However, the anode active material undergoes agglomeration as the cycle number is increased, because the particle size of the Sn and Si intermetallic compound increases. Thus capacity retention characteristic of the anode active material is gradually degraded.
To address these and/or other problems, U.S. Pat. No. 6,949,312 discloses an anode active material including an amorphous metal-carbon complex comprising Sn, a transition metal, and C. In addition, Japanese Patent Laid-Open Publication No. 2006-134784 discloses an Sn—Co—C complex obtained by mechanically milling an Sn—Co alloy and graphite, wherein the Sn—Co—C complex has very low crystallinity. However, there is still need to develop a method of improving the initial efficiency and cycle-life properties of an anode active material.